A second tornado has swept through Amberley in North Canterbury, damaging homes, felling trees and bring down power lines.

Amberley resident Leanne McTear was on her doorstep when the tornado struck her home, ripping the roof off and hurling it across the road.

"Everything went dark and there was just black dust and smoke whirling around,'' she said.

"There was a horrendous noise and I was waiting for the ground to move. It was really noisy and I didn't know what was going on. I saw bricks on the front lawn and Pink Batts everywhere. At the moment I am quite numb.''

Weather enthusiast and stormchaser Stephen Burrows said he saw a tornado near Amberley and a house near State Highway 1 had its roof ripped off.

"The roof has been completely stripped off. The roof was on the other side of the road,'' he said.

Blue Skies forecaster Tony Trewinnard saw the tornado form and travel from north of Amberley for about two or three minutes.

He said it was traveling at about 70 kilometres an hour and hurled debris about 100 metres into the air.

"There is no doubt in my mind that this was a tornado,'' he said."It was definitely a tornado. It wasn't hanging around. It was moving quite fast.''

Donna Graham has lived in Amberley for 20 years but has ''never seen weather like it''.

Graham and her husband Geoff witnessed a tornado above Amberley and saw ''trees shredded'' before hail stones battered their house.

''I was really frightened...it was just so dark looking and it was so close.''

The Grahams house faces south and Donna Graham said she had watched the ''black clouds hanging over the city'' since the late afternoon.

''I said to my husband that they were the sorts of clouds that form twisters...and I just couldn't believe what we were seeing.''

The couple photographed the tornado and filmed a short video before they lost power and decided to drive to a neighbour's house.

She said debris started hitting her home and she was scared the windows were going to smash.

''On one hand, it's really magnificent but I was ready to hide in the cupboard if I had to.''Graham said the extreme weather had shaken her up.

''I just honestly have never seen anything like it,'' she said.

LEESTON TORNADO

A mini tornado briefly formed near Leeston during the storm as well.

Weather enthusiast and ''stormchaser'' Stephen Burrows said he captured the small tornado on his video camera.

''It looked like a tornado in the Leeston area. I could see some dust being kicked up around it. It seemed to be about 100 metres wide, but quite weak,'' he said.

''It reached down to the ground. It wasn't a traditional, American one where it is a direct line from the cloud to the ground, but you could see it reached the ground and it was full of dust.

This morning, MetService forecaster John Crouch said parts of Canterbury could be affected by ''large, damaging hail and squally winds'' gusting up to 100 kmh.

Forecaster said some hail stones could be bigger than 2 cm in diameter. It could cause damage to crops and make driving conditions dangerous, Crouch said.

He advised people to move their vehicles undercover to avoid damage like broken windscreens.

People should to ''take care'' if they saw ''big, dark looking'' storm clouds approaching from the south or south-west.

Damaging hail storms usually affected parts of Canterbury two or three times each summer.

''An upper cold trough is expected to move across the South Island today making the atmosphere very unstable over southern New Zealand,'' Met Service's website says.

In December, Mid-Canterbury experienced hail stones up to 3cm in diameter that damaged crops and smashed windows in the Mayfield area.

The Ministry of Civil Defence and Emergency Management advises that as storms approach you should:

- Take shelter, preferably indoors away from windows;- Avoid sheltering under trees, if outside;- Move cars under cover or away from trees;- Secure any loose objects around your property;- Check that drains and gutters are clear;- Be ready to slow down or stop, if driving.

During and after the storm, you should also:

- Beware of fallen trees and power lines;- Avoid streams and drains as you may be swept away in flash flooding.